qemu-vmsr-helper: implement --verbose/-v

Similar to qemu-pr-helper, do not print errors from the socket handling loop
unless a --verbose or -v option is provided explicitly on the command line.

Sig

qemu-vmsr-helper: implement --verbose/-v

Similar to qemu-pr-helper, do not print errors from the socket handling loop
unless a --verbose or -v option is provided explicitly on the command line.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

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qemu-vmsr-helper: fix socket loop breakage

Between v5 and v6 of the series, the socket loop of qemu-vmsr-helper was changed to
allow sending multiple requests on the same socket. Unfortunately, the

qemu-vmsr-helper: fix socket loop breakage

Between v5 and v6 of the series, the socket loop of qemu-vmsr-helper was changed to
allow sending multiple requests on the same socket. Unfortunately, the condition
of the while loop is botched and the loop will never be entered. Clean it up, and
also unify the handling of error reporting.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

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tools: build qemu-vmsr-helper

Introduce a privileged helper to access RAPL MSR.

The privileged helper tool, qemu-vmsr-helper, is designed to provide
virtual machines with the ability to read specif

tools: build qemu-vmsr-helper

Introduce a privileged helper to access RAPL MSR.

The privileged helper tool, qemu-vmsr-helper, is designed to provide
virtual machines with the ability to read specific RAPL (Running Average
Power Limit) MSRs without requiring CAP_SYS_RAWIO privileges or relying
on external, out-of-tree patches.

The helper tool leverages Unix permissions and SO_PEERCRED socket
options to enforce access control, ensuring that only processes
explicitly requesting read access via readmsr() from a valid Thread ID
can access these MSRs.

The list of RAPL MSRs that are allowed to be read by the helper tool is
defined in rapl-msr-index.h. This list corresponds to the RAPL MSRs that
will be supported in the next commit titled "Add support for RAPL MSRs
in KVM/QEMU."

The tool is intentionally designed to run on the Linux x86 platform.
This initial implementation is tailored for Intel CPUs but can be
extended to support AMD CPUs in the future.

Signed-off-by: Anthony Harivel <aharivel@redhat.com>
Link: https://lore.kernel.org/r/20240522153453.1230389-3-aharivel@redhat.com
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

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